ChrisLX200

I also get some reflections around the edge but it's not too distracting. This vid is last Friday's RGB disaster, I'm hoping for better tonight - if not I'm giving up on RGB from here!

ChrisH

Good result Gina, you obviously have a darker sky than I do - Milky Way very obvious in your capture! I tend to use 8sec exposures with this Fujinon lens and that's good enough to show the quality of the seeing - I'm just processing last Fridays imaging run which was ruined by high Cirrus, the camera showed the potential problem well enough but I stupidly ignored it and went for RGB on M42. Captured data was useless sadly. I'll post the animation when it's uploaded to YouTube.

I tend not to use a Dome with this lens as it seems to be sensitive to reflections and distortions, so I just push the camera out the door of the Obs during an imaging run. There's a lot of glass pointing at the sky but it hasn't misted over yet - perhaps because the camera keeps it just warm enough to prevent it (or I've simply been lucky!).

ChrisH

You can safely leave the mount outside under a waterproof/breathable cover, but just make sure to protect all the electrics (sockets, PCBs etc) with a dose of ACF50 to prevent corrosion and resultant poor contacts. Also treat any metalwork liable to rust with the same (ie., parts made from ordinary steel or plated steel rather than stainless steel or anodised alloy). You should find that a big time saver.

ChrisH

That 1600 is really beginning to sing for you now Gina   Sounds like tough work dealing with all that data though!

ChrisH

3 minutes ago, Gina said:

That thread is about long exposures so not really relevant - most I use is 2m.  Thanks all the same

Well it was his use use of the offset parameter in shorter (90-120s) I thought interesting...

Anyway, here are the gain settings I use, with a 150mm aperture at f/4:
Optimal SNR: Gain 75/Offset 15, 480-600s
Balanced SNR/Resolution: Gain 139/Offset 30, 210s
High Detail/Resolution: Gain 200/Offset 60, 90s

ChrisH

I don't know if you've read this thread Gina: http://www.astrobin.com/forum/c/group-forums/zwo-asi1600mm/gain-and-offset-settings-for-long-exposure/

Jon Rista is a good guy who knows what he's doing so his comments particularly may be helpful.

ChrisH

Just looked at mine and it's cloudy - and likely to remain so (after saying for the past 3 days it would be clear).

ChrisH

As you say, all have their faults and when tested some will perform better than others. So who do you pay the bribe to in order to ensure you get the pick of the bunch? 

ChrisH

1 hour ago, Horwig said:

shouldn't think that 20 years is old in Rayburn terms, don't they go on for ever?

My gas boiler is more than 25years old, I thought about replacing it when I had a leak earlier in the year and advice (from a plumber) was  - don't bother, old ones are easy to repair but new ones don't last anywhere near as long! The problem with mine was the seal around a steel plate had just rotted, the bolted-on plate covered a core hole in the cast iron boiler. The leak though had dripped onto the main circuit board which died as a consequence, yet I managed to get a replacement cheaply off Ebay. The only other problem I've had with it over the years is a vacuum switch which turns on the gas valve only when the extractor fan is running - I bought a spare off Ebay only to find it was a thin plastic pipe to the valve which had split. I'll save the spare valve in case I need it over the next 25 years...   Oh, and a few years ago I had to put some engine oil onto the bearings of the extractor fan motor as it had begun to squeak..

ChrisH

That's bad luck guys    hope it's a simple fix. Not what you want at any time of year but especially now as it's just starting to get colder.

ChrisH

21 minutes ago, Stub Mandrel said:

It's fundamentally because. the scope itself is not just moved a foot or two to one side, it's rotated through 180 degrees.

I think we have a Missed Point Error in Line.1 here    We know it's been flipped 180deg but frames should still line up (just 180deg out), but folk are reporting residual rotation of a degree or two which cannot be accounted for..

ChrisH

3 hours ago, Stub Mandrel said:

I fear you all have bit too much confidence in how well you align your scopes.

See below, if your scope, in its rings, is perfectly aligned with the dec axis (1a), a rotation (1b) followed by a flip (1c) will leave the scope pointing at the same spot.

If it is not fitted exactly parallel to the DEC plane of rotation (2a), the RA rotation (2b) and DEC flip (2c) will leave it pointing at a very different place, at least with my exaggerated five-degree misalignment.

Clearly a 1-minut misalignment, too small to see, would give a 2-minute error in pointing, enough to give two mis-aligned images.

There is no need to invoke an inaccuracy in the mount itself.

 

 

That's pretty much what I said earlier but the point is not the misalignment, that is easily corrected by plate-solving back onto target (i.e., the same centre of frame), but there remains some residual rotation comparing each side of the mount. It's the rotation that is the weird issue.

ChrisH

2 hours ago, vlaiv said:

Not sure that I'm convinced with this argument.

Cone error - in essence same thing as pointing to a different part of the sky. Only important in the terms - goto / mount / computer thinks that scope is pointing to a certain place, and the scope knows it's pointing somewhere else. After meridian flip, frame will be rotated 180 degrees and point where scope is pointing will be "rotated" 180 degrees - meaning it will flip cone error to other side - it will not contribute to FOV rotation - only offset - this is corrected with RA/DEC offset (which does not rotate FOV).

Orthogonality of camera being X/Y orientation to RA/DEC? - no impact on meridian flip as it rotates FOV by 180 no matter how it's oriented - if it's 30 degs to "horizontal" (being RA) - after 180 deg rotation it will continue to be 30 degs to horizontal.

There's more than one way of getting Cone Error - one way is if the scope does not sit orthogonal to the DEC axis (the saddle may not be orthogonal to the DEC axis), another is if the DEC axis itself is not orthogonal (perfectly @ 90deg) to the RA axis. Consider the latter - the pointing error will be doubled after a meridian flip (if the pointing offset was 1deg East before the flip it will be pointing 1deg West afterwards thus requiring a 2deg movement in RA to get back on target). So you have 2 different RA positions needed to point at the same place in the sky leading to a rotational offset.

ChrisH

Looks good - well done!   Maybe a tad bright?

ChrisH

4 minutes ago, Gina said:

Just had a look outside and the sky has cleared   So which DSO to image...

I think you could safely hold your breath until the clouds arrive - I've looked at Sat24   Nothing but cloud and rain here so I'm taking new sets of Darks and Flats...

ChrisH

I'm not at all sure about cone error either, just something off the top of my head

I do know my camera is not set at exactly 90deg to the scope centre line, it's just approximately so - and I try not to move it between sesssions as I know I won't get it precisely back in place (sheer idleness I suppose!).

Anyway, the 10-Micron is very precise and it will flip and exactly line up the centre of the frame afterwards - no need to plate solve to get that accuracy. When I later come to stack subs from E and W of the pier they often align with no artifacts at all - but sometimes there is a lateral shift of 1 or 2 pixels which leaves parallel dark line(s) on one side or the other. It's no big deal and I know the cause of that (usually not precisely re-balancing at the start of the imaging session, and re-using the old mount model. With a new model generated just prior to starting the session the alignment is perfect).

So what does that tell you? Firstly, under ideal conditions then you won't get rotation. If you ARE getting rotation between E and W sides of the mount then clearly something else is a play - either flexure or some pointing error. How flexure would translate to rotational mis-alignment I can't envisage, but what else is there? I would ask if the rotation is progressive - does it increase the further away from the meridian you get after the flip.

ChrisH

1 minute ago, steppenwolf said:

There are only two conditions under which there is no rotation after a flip:-

1. when the long side of the sensor runs exactly parallel to the RA axis (90 degrees)      or

2. when the long side of the sensor runs exactly parallel to the DEC axis (0 degrees)

At any other orientation, there will be an error of double the variance from the above.

? don't understand that - a flip just rotates by 180deg and that's that, doesn't matter what angle the camera is at. If that was not true then I wouldn't be able to stack subs from East and West sides of the mount without rotation showing, but I can.  Maybe cone error will add some rotation though (just a thought of the top of my (shiney) head )

ChrisH

It's one of them new-fangled aeroplane things...

ChrisH

Same here... but supposed to improve after midnight. Trouble is there's a danger of a spot of rain (or even snow here) so too risky leaving everything outside.

ChrisH

1 minute ago, Gina said:

My sub length is 60s alias one minute   But I need hundreds of them for a good result!

I reckon you can really benefit from conditions like these, those short gaps are useful to you   It's definitely not a night to be sat outside though - too flippin cold!

ChrisH

I'm watching those clouds (well OK, not those clouds) here, it's going to be one of those frustrating nights where the clear gap between clouds is 5 minutes less than your sub length - whatever it might be.

ChrisH

7 minutes ago, Stub Mandrel said:

I keep reading posts from people who are spending ages 'building their models' I assume these aren't airfix kits, so what are they? Mapping errors in the mount?

Yes, pointing models - they map the flexure/errors in pointing accuracy, and that is also fed back into the tracking algorithm when using dual-axis tracking. Basically you point to lots of random places in the visible sky and plate-solve a quick (4seconds in my case) image, the result is then compared to where the mount 'thinks' it is pointing and the error noted and included in the model. Just run one myself earlier tonight, waste of time trying to image anything with all the flashes and bangs so I updated the mount model instead. Imaging now though.

ChrisH

35 minutes ago, Gina said:

Found the way to access the setup screen - press Delete while powering up.  However, the boot order options do not include booting from USB - just [Windows Boot Manager] which was what it was set to and two UEFI options both of which boot into a shell but whether that is of any use I don't know.  Took a photo of the display which I've attached.

What's option 3? looks like a storage device - but it's below Windows boot manager so won't be seen...

ChrisH

Yes, you will get full speed out of your cable Cat5e or Cat6 over that short distance. It's better to use decent cable if you have it, one designed for use outdoors. Lay in a spare as well if you're going underground with it, the small extra cost may save a lot of hassle at some point in the future!  I laid two underground from Obs to pier, but just one to the house (although that one runs overground so easier to replace if needed).

ChrisH

These are what I used - much thicker cable than normal https://www.amazon.co.uk/gp/product/B00FSAL592/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

1 hour ago, Gina said:

Looking at figures :-  The session last night produced 18GB of data which I'm now moving to SD card taking an estimated 26m then I will have to go back out and bring the card indoors and move the files onto the HD of the desktop.  Using Gigabit LAN I should be able to transfer about 120MB/s = 2GB/m so 18GB should take 9m to transfer across.  Or is getting a real 1 Gigabit data transfer with gigabit LAN being optimistic?

Much depends on the cabling and how many connections/junctions/other sockets connected between, but the quoted throughput(s) for powerline connections are very optimistic indeed. Maybe they are achievable under ideal conditions but I never got got anywhere near the 500Mbit/sec quoted for mine (like about 20% of that...). It was that which prompted me to lay in a long ethernet cable from the Obs to the router in the house.

ChrisH